type LogLevel = "debug" | "info" | "warn" | "error";
interface LogEntry {
timestamp: string;
level: LogLevel;
message: string;
[key: string]: unknown;
}
class Logger {
private logLevel: LogLevel = (process.env.LOG_LEVEL ||
"info") as LogLevel;
private shouldLog(level: LogLevel): boolean {
const levels: Record<LogLevel, number> = {
debug: 0,
info: 1,
warn: 2,
error: 3,
};
return levels[level] >= levels[this.logLevel];
}
private format(entry: LogEntry): string {
return JSON.stringify(entry);
}
private log(level: LogLevel, message: string, metadata?: unknown) {
if (!this.shouldLog(level)) return;
const entry: LogEntry = {
timestamp: new Date().toISOString(),
level,
message,
...(metadata && typeof metadata === "object" ? { metadata } : {}),
};
// MCP servers must write logs to stderr, not stdout
process.stderr.write(this.format(entry) + "\n");
}
debug(message: string, metadata?: unknown) {
this.log("debug", message, metadata);
}
info(message: string, metadata?: unknown) {
this.log("info", message, metadata);
}
warn(message: string, metadata?: unknown) {
this.log("warn", message, metadata);
}
error(message: string, metadata?: unknown) {
this.log("error", message, metadata);
}
}
export const logger = new Logger();
